Cosomological Constant

[Amr Morsi]

Hi All,

 

Some news are being transmitted now, that the cosomological constant, these time in the Universe, is passing through an abrupt change in value. Have anyone have any idea about that?

 

Thanks in advance.

[[Tycho?]]

What are you talking about?

[ajb]

It is known as a period of inflation.

 

It looks like the universe is going through a second stage of inflation.

[lakmilis]

He, c changing would love that...would that not make SR's confirmed experimental data of no aether interesting....as if c changes in 'vacuum' , space must have a property of a medium in similar ways as other denser medias do to light?

 

kind of has some issues when you mention that with another thread i just started where I am wondering a bit about the exact properties of space with regards to temperature or heat density.

[lucaspa]

Hi All,

 

Some news are being transmitted now, that the cosomological constant, these time in the Universe, is passing through an abrupt change in value. Have anyone have any idea about that?

 

Thanks in advance.

 

It was thought that the cosmological constant was 0. Recent data shows that lambda has a positive value. However, I haven't seen anything about an "abrupt change in value". Rather, it is our human measurement that has been "abrupt" in that we have "abruptly" shown that the cosmological constant is not 0.

 

http://super.colorado.edu/~michaele/Lambda/lambda.html

http://www.astro.ucla.edu/~wright/cosmo_constant.html

[Martin]

It was thought that the cosmological constant was 0. Recent data shows that lambda has a positive value....

http://super.colorado.edu/~michaele/Lambda/lambda.html

http://www.astro.ucla.edu/~wright/cosmo_constant.html

 

I agree completely with lucaspa, and also approve of the ucla.edu source.

the colorado.edu source is also probably good, I just havent checked it.

 

the big change came in or around 1998

before 1998 most astronomers assumed this quantity (which occurs in the equation for gravity in General Relativity) was zero.

In 1998 several teams reported supernova observations indicating much to everyone's surprise that the quantity was not zero but slightly positive.

 

If the estimated value of the cosmological constant (denoted by greek letter Lambda) is expressed as an energy density it comes out to be a density of about 0.6 joule per cubic kilometer.

 

a joule is a small amount of energy, like what is involved in raising a book a few centimeters

 

or if you count energy in food Calories, a joule is roughly 1/4000 of a food Calorie (1/4 of a lab calorie).

 

so you can picture the energy density associated with Lambda as this small amount of energy, 0.6 joule, spread out in a cubic kilometer---a very big volume.

 

that energy density is sometimes called the "dark energy" density----just a way of quantifying Lambda.

 

why there is a nonzero Lambda, and whether it really should be thought of as an energy density of some kind, is not very well understood.

[lucaspa]

the big change came in or around 1998

before 1998 most astronomers assumed this quantity (which occurs in the equation for gravity in General Relativity) was zero.

In 1998 several teams reported supernova observations indicating much to everyone's surprise that the quantity was not zero but slightly positive.

 

And now I will agree with Martin. This is what I referred to as "abrupt" in that humans found that the cosmological constant (lambda) was not 0. Other types of measurements have confirmed the original measurements.

 

that energy density is sometimes called the "dark energy" density----just a way of quantifying Lambda.

 

why there is a nonzero Lambda, and whether it really should be thought of as an energy density of some kind, is not very well understood.

 

I would like to emphasize this. There is a lot of discussion among physicists as to the cause of the nonzero lambda, but no consensus as yet. So we know lambda is not zero, but not why. Everyone, just be patient and wait while the physicists figure it out. It may take a while.

[grifter]

The cause of the non-zero [math]\lambda[/math] is derived from non-zero vacuum energy density causing the longrange repulsion effect resulting in the accelerating expansion of the Universe.

[lucaspa]

double post

[lucaspa]

The cause of the non-zero [math]\lambda[/math] is derived from non-zero vacuum energy density causing the longrange repulsion effect resulting in the accelerating expansion of the Universe.

 

You have this backwards. The accelerating expansion of the universe tells us that lamda is not zero. However, the cause of the non-zero lambda is not known. I would refer you back to Martin here: "why there is a nonzero Lambda, and whether it really should be thought of as an energy density of some kind, is not very well understood."

 

"Vacuum energy density" is one hypothesis for the cause of the non-zero lambda. But there are other hypotheses.

 

Determining the cause of the non-zero lambda is where I urge caution and patience. Just wait and let the physicists fight it out until they reach consensus.

[lucaspa]

He, c changing would love that...would that not make SR's confirmed experimental data of no aether interesting....as if c changes in 'vacuum' , space must have a property of a medium in similar ways as other denser medias do to light?

 

The experiment falsifying the aether was done in the 1880s, over 20 years before Einstein published Special Relativity. So, SR did not "confirm" the experimental data of no aether. Instead, SR is a theory that doesn't require a medium for light to move thru.

 

The cosmological constant does not have anything to do with the speed of light in a vacuum. So getting a positive lambda doesn't affect c.

[Severian]

Determining the cause of the non-zero lambda is where I urge caution and patience. Just wait and let the physicists fight it out until they reach consensus.

 

It is actually a bit worse than that. The Standard Model predicts a non-zero value of lambda (coming from the vev of the Higgs field), but unfortunately it is 120 orders of magnitude. You then have to put in a very large opposite sign contribution by hand, but of course, that is a fine tuning problem, known as the cosmological constant problem.

[lakmilis]

The experiment falsifying the aether was done in the 1880s, over 20 years before Einstein published Special Relativity. So, SR did not "confirm" the experimental data of no aether. Instead, SR is a theory that doesn't require a medium for light to move thru.

 

The cosmological constant does not have anything to do with the speed of light in a vacuum. So getting a positive lambda doesn't affect c.

 

I know Lucaspa, but experiments were still tried later...and my comment on c was not to do with lambda, I just saw someone mentioning above it was changing or so? well yes, SR says no medium is needed as such... but he (onestone) did state light must take the shortest path which due to curvature is curvilinear in minkowspi space...in other words, mass does not affect light dircetly but seemingly by curving space , so vacuum affects the path of light...

 

Since this is an interaction, I simply mentioned the ideas of aether (or today we would be babbling abt vacuum energy density bla bla) as a changing c if this was/is the case, would be very interesting to know about.

 

[lucaspa]

It is actually a bit worse than that. The Standard Model predicts a non-zero value of lambda (coming from the vev of the Higgs field), but unfortunately it is 120 orders of magnitude. You then have to put in a very large opposite sign contribution by hand, but of course, that is a fine tuning problem, known as the cosmological constant problem.

 

WHOA! We have 2 problems:

 

1. The cause of lambda in general.

2. Why the magnitude does not correspond to that calculated from the Standard Model. BTW, I assume you mean "120 orders of magnitude higher than the measured lambda". That, of course, may be a problem for the Standard Model (theory).

 

The post I was responding to seemed to think the cause of lambda was established. It isn't, and my response was limited to that.

 

The magnitude of lambda is a related, but separate problem. Whatever is determined to be the cause, a test of that cause is going to be that it gives the value we observe.

 

Altho, I have seen it mooted that lambda may not be a constant, but may vary as the universe ages. Robert Caldwell and Paul J. Steinhardt are 2 proponents of this hypothesis.

 

But again, my caution to let the physicists fight it out remains. I am just noting the problem and listing a few of the possible solutions.

 

I'm quite content to sit back, pop some popcorn, open a Coke, and watch the physicists figure it out. When they declare a winner, I'll accept that.

[lucaspa]

I know Lucaspa, but experiments were still tried later...and my comment on c was not to do with lambda, I just saw someone mentioning above it was changing or so?

 

That was YOU mentioning that c was changing! And no, the discovery that lambda is positive does not affect c = speed of light in a vacuum.

 

well yes, SR says no medium is needed as such... but he (onestone)

 

Look, that isn't cute. It's just juvenile. Just say "Einstein". That's his name, no need to do a literal translation to English.

 

did state light must take the shortest path which due to curvature is curvilinear in minkowspi space...in other words, mass does not affect light dircetly but seemingly by curving space , so vacuum affects the path of light...

 

Non-sequitor. As you said, the curve of space affects the path of a photon, but not vacuum itself. If space is expanding, then that expansion affects the path of a photon.

 

Since this is an interaction, I simply mentioned the ideas of aether (or today we would be babbling abt vacuum energy density bla bla) as a changing c if this was/is the case, would be very interesting to know about.

 

Aether and vacuum energy are 2 very different things. Vacuum energy is the term used as what is responsible for the Casimir effect. It is the idea that "vacuum" is not empty of matter, but instead has a constant "bubbling" of virtual particles. Virtual particles pop into existence for about 10^-21 seconds and then disappear again. This seems to happen at a uniform rate everywhere. Because the virtual particles disappear, they do not constitute a "medium" in the way aether was using the term -- a permanent substance that permeated the universe. Virtual particles are very discrete and VERY temporary.

[lakmilis]

Strange, I was sure when I read this thread as it was starting I saw someone mentioning c was changing..maybe I took it from another related article or even from a different thread. I'm sorry.

 

So I am juvenile at times.

 

On the final issue however, we go into that which is so debatable on a semantic level. I should of not used the word aether to begin with I admit, and just stuck with vacuum energy density. What I am referring to, is this difference of space-time 'vacuum' and that which is 'beyond' (as in conceptual questions inherent to the way our minds work, regardless of if the universe is open or closed..that which space-time expands into so to speak).

 

Frame-dragging and change in c would indeed indicate that space-time / 'vacuum' must have since information on it is predictive, have physical properties where vacuum should have some energy density.

 

Like I said, I apologize for using the word aether as it was logical that people would have different associations to its [historical] definition. Like you say aether -- a permanent substance which permeated the universe.

 

Whilst what I meant was more like aether -- a permanent substance which is the universe.

 

Non-sequitor...hmm, well you say if space is expanding, then the expansion affects the photon path... So if it affects the path, the expansion also can affect the 'static' velocity of light in this vacuum. What do you think?

 

But while I'm at it, does anyone know if the gravity probe B has had its results released?

[lucaspa]

On the final issue however, we go into that which is so debatable on a semantic level. I should of not used the word aether to begin with I admit, and just stuck with vacuum energy density. What I am referring to, is this difference of space-time 'vacuum' and that which is 'beyond' (as in conceptual questions inherent to the way our minds work, regardless of if the universe is open or closed..that which space-time expands into so to speak).

 

There is no "beyond" in the frame we are discussing. Since matter and energy are 2 different forms of the same thing (E=mc^2), the "vacuum energy" simply means that energy > 0 where there is no matter (vacuum). This energy can be "borrowed" to have some of the energy expressed as matter by Einstein's famous formula. As long as the energy is "paid back" in a short time. Looked at another way, the energy in space can fluctuate between energy and matter over very short time frames.

 

If energy is added to the system -- say by a particle accelerator colliding particles together -- then the virtual particles can become permanent.

 

Whilst what I meant was more like aether -- a permanent substance which is the universe.

 

You may be thinking of spacetime, which is a "permanent substance" (altho not matter) that is part of the universe. Remember, without spacetime, there is no universe.

 

Non-sequitor...hmm, well you say if space is expanding, then the expansion affects the photon path... So if it affects the path, the expansion also can affect the 'static' velocity of light in this vacuum. What do you think?

 

No. Think of this as an analogy: you are driving from New York to Pittsburgh at 65 mph. Along the way you decide to go to Cleveleand instead. You are still going 65 mph but the distance (space) that you must cover has increased. Same with the expanding universe. c remains constant but the length and shape of the path changes.

 

But while I'm at it, does anyone know if the gravity probe B has had its results released?

 

Preliminary results are in and on the web: http://einstein.stanford.edu/

"Everitt and his team are poised to share what they have found so far — namely that the data from the GP-B gyroscopes clearly confirm Einstein's predicted geodetic effect to a precision of better than 1 percent. However, the frame-dragging effect is 170 times smaller than the geodetic effect, and Stanford scientists are still extracting its signature from the spacecraft data. The GP-B instrument has ample resolution to measure the frame-dragging effect precisely, but the team has discovered small torque and sensor effects that must be accurately modeled and removed from the result. "

[lakmilis]

I agree mainly with all you say Lucaspa. And thanks about the probe (found the main site by now, was the frame dragging im interested in).

 

Only one thing. You don't need to use analogys of space-time as driving and changing vector and without space-time continuum there is no universe.

 

What I was trying to point out is this:

 

Imagine framedragging so strong that curvature of space(-time) is even larger than purely by gravitational motion of mass.. In such an area c does not need be constant. As I saw in another post, someone was deducing something similar about radial and transverse photon velocity around a black hole I think.

 

Anyway, why I stated it in this thread was due to since it had to do with the movement of space-time , then it caught my eye.

 

Obviously the problem with lambda in cosmology contra QM, makes digressions like mine was, not surprising.

 

Anyway, like I said , I still thought I saw the c change here, so I am somewhat confused about that; will continue postings on other threads as it seems like I trod on people's toes with this.

 

ps. There is never a 'beyond' when one is discussing a closed frame

[etrader]

Cosmological constant is the biggest Einsten mistake, as he confessed.

 

Are you seeking for a chance to overcome ?

[lucaspa]

Cosmological constant is the biggest Einsten mistake, as he confessed.

 

Are you seeking for a chance to overcome ?

 

Let's put this in historical context. When Einstein did the Relativity equations, it was thought that the universe was static. Since gravity was a solely attractive force, the equations needed lambda (the cosmological constant) as a positive quantity to counter the force of gravity and keep the universe from collapsing. The other aspects and predictions of Relativity were so strongly supported that this "fudge factor" was accepted.

 

In the 1920s it was found that the universe was NOT static, but expanding. Therefore the cosmological constant was no longer needed in the equations and people just set it = 0. This is when Einstein called it a "blunder". It was thought that the expansion came from the Big Bang and was slowing as gravity countered the original expansion. The question was whether there was enough matter to generate enough gravity to halt the expansion or not.

 

HOWEVER, starting in 1998 data started coming in that showed that the expansion was accelerating. This meant that the cosmological constant was not zero and NOT a "blunder", but actually represented a real phenomenon. For the wrong reasons, Einstein got it right.

[lucaspa]

What I was trying to point out is this:

 

Imagine framedragging so strong that curvature of space(-time) is even larger than purely by gravitational motion of mass.. In such an area c does not need be constant.

 

It sounds like you are trying to use frame dragging to revive the Lorentz contraction. The problem is that you have to change c just enough and differently in relation to earth's motion in space to get the results of the Michelson-Morely experiments. That smacks of an ad hoc hypothesis and one that won't work. Since earth's rotation, and thus its frame dragging, is constant around the circumference, it should give different measurements for the velocity of c at different points on the earth's surface. That doesn't happen.

[astrocat]

Cosmological constant is the biggest Einsten mistake, as he confessed.

 

I agree. I cannot understand how anybody could become involved in Einstein's Cosmological Constant knowing that he, Einstein, later denounced the Cosmological Constant as the greatest blunder of his career. What is going on here? I am suspicious!

[ajb]

I agree. I cannot understand how anybody could become involved in Einstein's Cosmological Constant knowing that he, Einstein, later denounced the Cosmological Constant as the greatest blunder of his career. What is going on here? I am suspicious!

 

Are you suggesting that we do not pursue the possibility of a cosmological constant because Einstein thought that it should vanish?

 

If so then this is absurd.

 

Two points,

 

i) Einstein died in 1955 well before observational cosmology developed in to the science it is today.

 

ii) Einstein always was unhappy with quantum mechanics and did not actively work on quantum field theory. Having a zero value parameter in quantum field theory is awkward and "unnatural".

 

Einstein although well respected is not held in some kind of awe by practising scientists. Generally, Einstein's ideas need to be re-examined from a modern view point.

[Martin]

the journal called General Relativity and Gravitation has a special issue devoted to Dark Energy coming out.

 

So far, I have read only the article contributed by Martin Bojowald.

 

He explains the acceleration in distance-expansion as a quantum correction to the gravitational field---generic in Loop Quantum Cosmology (and possibly also in a broader class of quantum cosmologies).

 

He points to ways to test the result by observing the acceleration history in more precise detail.

 

http://arxiv.org/abs/0705.4398

" While observational cosmology has recently progressed fast, it revealed a serious dilemma called dark energy: an unknown source of exotic energy with negative pressure driving a current accelerating phase of the universe. All attempts so far to find a convincing theoretical explanation have failed, so that one of the last hopes is the yet to be developed quantum theory of gravity. In this article, loop quantum gravity is considered as a candidate, with an emphasis on properties which might play a role for the dark energy problem. Its basic feature is the discrete structure of space, often associated with quantum theories of gravity on general grounds. This gives rise to well-defined matter Hamiltonian operators and thus sheds light on conceptual questions related to the cosmological constant problem. It also implies typical quantum geometry effects which, from a more phenomenological point of view, may result in dark energy. In particular the latter scenario allows several non-trivial tests which can be made more precise by detailed observations in combination with a quantitative study of numerical quantum gravity. If the speculative possibility of a loop quantum gravitational origin of dark energy turns out to be realized, a program as outlined here will help to hammer out our ideas for a quantum theory of gravity, and at the same time allow predictions for the distant future of our universe.

 

24 pages, 2 figures, Contribution to the special issue on Dark Energy by Gen. Rel. Grav"

[lucaspa]

I agree. I cannot understand how anybody could become involved in Einstein's Cosmological Constant knowing that he, Einstein, later denounced the Cosmological Constant as the greatest blunder of his career. What is going on here? I am suspicious!

 

You obviously didn't read my post giving the history of this. We become involved in the cosmological constant because of the data. Look at the last paragraph:

 

"Let's put this in historical context. When Einstein did the Relativity equations, it was thought that the universe was static. Since gravity was a solely attractive force, the equations needed lambda (the cosmological constant) as a positive quantity to counter the force of gravity and keep the universe from collapsing. The other aspects and predictions of Relativity were so strongly supported that this "fudge factor" was accepted.

 

In the 1920s it was found that the universe was NOT static, but expanding. Therefore the cosmological constant was no longer needed in the equations and people just set it = 0. This is when Einstein called it a "blunder". It was thought that the expansion came from the Big Bang and was slowing as gravity countered the original expansion. The question was whether there was enough matter to generate enough gravity to halt the expansion or not.

 

HOWEVER, starting in 1998 data started coming in that showed that the expansion was accelerating. This meant that the cosmological constant was not zero and NOT a "blunder", but actually represented a real phenomenon. For the wrong reasons, Einstein got it right."